Frequency yariation response circuit



Jan. 1946. B. NOVlKS ET AL 2,393,400

FREQUENCY VARIATION RESPONSE CIRCUIT Filed Feb. 1, 1943 |NVENTOR BER5NOV/K5 6: CAND/DO A. VAIO ATTORNEY Patented Jan. 22, 1946 FREQUENCYVARIATIQN BESPQNSE CIRCUIT Bers Noviks and- Candido Alberto Vaio, BuenosAires, Argentina, 'assignors' to Tran'sradlo Iiitemacional CompafiiaArgentinade Telucomunicaciones, Sociedad' Anonima', Buenos Aires,Argentina, an Argentine company Application February 1, 1943, Serial No.474,356

In Argentina November 30,1942

9 Claims.

This invention relates to high frequency variation response circuits,and more particularly to frequency response networks of a type utilizingchanges in phase relations ofv primary and secondary circuit voltageswhich occur in coupled tuned circuits when the applied high frequencyenergy departs from the resonance frequency of the tuned circuits.Circuits of this general type are commonly referred to as frequencydiscriminator circuits, attention being invited to Seel'ey Patent No.2,121,103, granted June 21', 193.3, and Usselman Patent No. 1,794,932,granted March 3, 1931, for descriptions of known types of discriminatorcircuits.

The present invention is an alternative type of high frequency variationresponse circuit employing the following features: (1) A pair ofdiscriminator and detector systems, each involving two rectifiers and adirect current amplifier. (2) A glow discharge tube associated with eachdiscriminator system which is conductive only when the frequency is offthe assigned value. (3) A motor arrangement having a two-phase windingwhich is adapted to rotate in either of two directions under control ofthe pair of discriminator systems. Although the preferred form of theinvention employs all of these features, obviously the invention is notlimited to the precise arrangements shown and described hereinafter.

The present invention finds particular application wherever there isneed for a frequency re sponse network which supplies a rapidlyincreasing output of one polarity or another according, to whether thefrequency of the applied energy departs in one direction or the otherfrom a mean frequency by more than a predetermined amount. The highfrequency variation response circuit of the invention can be used in anautomatic frequency control system, or in a receiving system employed toreceive frequency modulated carrier waves. If used to receive frequencymodulated carrier waves, the frequency variation response network isutilized in connection with the detection of frequency modulated waves,as known in the art.

A more detailed description of the invention follows in. conjunctionwith a drawing whose single figure illustrates a preferred embodiment ofan automatic frequency control circuit in a superheterodyne receiver. 7

Referring to the drawing, there is shown a double detection receiveremploying an energy collector in the form of an antenna A, a radiofrequency amplifier B for amplifying the energy collected on theantenna, a first detector C, which beats with energy produced from afirst local oscillator D to produce an intermediate frequency which isfed to an intermediate frequency amplifier E. Energy from theintermediate frequency amplifier 'E is then fed to a second detector Ewhere it beats with energy from a second local oscillator G to produce asecond and lower intermediate frequency wavewhich is passed'on toband-pass intermediate frequency amplifier H. The'energy" passingthrough band-pass intermediate frequency amplifier H is then in thesecond intermediate frequency amplifiers K and L. A transformer T1 isemployed to couple the output from amplifier K to the input of amplifierL. Local oscillator G is controlledajs to frequency by means of a link Nwhich is geared to a two-phase modified Telechron motor M, the latterbeing controlled through coupling tubes P1,,P2, glow discharge devicelimiters Q1, Qzfdirect current amplifiers S1, S2, and pairs of detectorsV1, V2, in the manner describedhereinafter; In practice, the automaticfrequency control from motor M is applied to the second beat frequencyoscillator G by means of a small condenser (indicated diagrammatically)located across ,theflmain tuningcondenser (not shown). The motor islinked to the Vernier condenser of the oscillator G through a suitablereduction gear.

This verniercondenser, by way of example, can

be rotated through a ten to thirty-sixreduction gear with a rotationspeed of about 3.6 revolutions per minute. In the output ofthe secondintermediate frequency amplifier detector there is provided atransformer Tz' comprising a primary winding i coupled to twosecondarywindings 2 and 3. Each of these windings cooperates with acondenser, individual thereto, to form a tunedc'ircuit. These-tunedcircuits (as well as the tuned circuits including the coilsoftransformer T1) are tuned to the mid-band frequency to be passedthrough the system. The midpoint of primary winding I, itshould benoted, laconnected through a-lead 5 to the mid points" of the secondarywindings 2 and 3 to'supply in-phase potentials to the'pairs of detectorsV1, V2. The primary winding l is also inductivelycoupledto the secondarywindings-2 and 3 to'supply antiphase potentials to the two detectors ofeach pair V1 or V2. 'The outputs ofthe detectoravrand V2 arerespectively coupled to the grids of'direct current vacuum tubeamplifiers-$1,821 A suitable radio 'frequency choke coilt connectsthemld point of each output circuit of each pair of detectors to themidpoint of the associated jsecondary coil of the transformer T2. Theanodes of the direct current amplifiers S1, S: are connected togetherthrough suitable resistors and each anode is coupled to a limiter Q1 orQ; comprising a glow discharge voltage regulator type tube. Theselimiter tubes Q1, Q2 are arranged to be conductive when the frequency ofthe local oscillator is on the assigned value and one of the tubes willbe conductive and the other non-conductive when the frequency is off theassigned value, depending upon whether the frequency is either above orbelow the assigned value. The coupling tubes P1, P2 couple the limitertubes to coil windings I and 8 on the two-phase induction motor. It willthus be noted that the coils I and 8 are energized by alternatingcurrent via the two coupling tubes P1, P2, in turn excited through thelimiters Q1, Q2 from the direct current amplifiers S1, S2, the latterbein coupled to the discrimi nator circuits constituted by 2, V1 and 3,V2. When the frequency is on the assigned value, the alternatingcurrents through coils 1 and 8 will be equal and opposite. When,however, the frequency is of" the assigned value a predetermined amount,the current through one coil will be cut 1;

off, because the space current through its associated coupling tube willbe cut off, While leaving unaltered the current through the other coil.In effect, the space path of each coupling tube provides a seriesresistance for its directly connected coil winding on the modifiedTelechron motor. A third coil 9 on the motor M obtains its driving forcefrom the alternating current supply line Y. This supply line alsoprovides heating current for the filaments of the coupling tubes and asuitable polarizing voltage for the anodes of the coupling tubes throughthe coils 1 and 8. The modified motor M is, in effect, a two-phase motorwhich operates by virtue of the difference in current through thewindings l and 8. The value of this current difference is dependent uponthe amount of change of impressed frequency from the assigned frequencycorresponding to the resonance frequencies of the tuned circuits l, 2,3.

In one embodiment of the invention successfully tried out in practice,the first oscillator D was arranged to beat the incoming signal down tothe first intermediate frequency of 465 kilocycles per second, and thesecond oscillator G was arranged to beat the first intermediatefrequency energy down to a second intermediate frequency of 65kilocycles per second. The sec ond intermediate frequency amplifiertubes K and L were 68.17 and 68K? tubes, respectively. The pair ofdetectors of circuits V1 and V2 employed 6H6 tubes. The direct currentamplifier tubes S1, S2 were 6SF5 tubes. The limiters Q1, Q2 were RCA 991voltage regulator tubes which had a 30 db. limiter characteristic. Thecoupling tubes P1, P2 were 6V6 tubes. The motor M was a General Electricclock motor.

What is claimed is:

1. In a frequency variation response network, a first resonant circuit,second and third resonant circuits inductively coupled to the firstresonant circuit, connections from the electrical centers of said secondand third resonant circuits to a point on said first resonant circuit,said resonant circuits being tuned to the same frequency, an alternatingcurrent input circuit coupled to said first resonant circuit, a pair ofrectifiers having corresponding electrodes connected across said secondresonant circuit, another pair of rectifiers having similarcorresponding electrodes connected across said third resonant circuit, afirst direct current amplifier coupled to the outputs of one pair ofrectifiers and a second direct current amplifier coupled to the outputsof the other pair of rectifiers, and a two-phase induction motor havingdifferent windings the currents in which are under the control of saiddifferent direct current amplifiers, and a third winding coupled to adriving source of alternating current ener y, whereby a difference inthe outputs of said direct current amplifiers causes said motor torotate in either of two directions depending upon the sense of departurein frequency of the applied alternating current waves from the resonancefrequency of said tuned circuits.

2. In a frequency variation response network, a first resonant circuit,second and third resonant circuits inductively coupled to the firstresonant circuit, connections from the electrical centers of said secondand third resonant circuits to a point on said first resonant circuit,said resonant circuits being tuned to the same frequency, an alternatingcurrent input circuit coupled to said first resonant circuit, a pair ofrectifiers having corresponding electrodes connected across said secondresonant circuit, another pair of rectifiers having similarcorresponding electrodes connected across said third resonant circuit,a. first direct current amplifier coupled to the outputs of one pair ofrectifiers and a second direct current ainplifier coupled to the outputsof the other pair of rectifiers, a glow discharge device limiter incircuit with the output of each direct current amplifier, a couplingtube having its input circuit connected to each limiter, and a motorhaving different windings the currents in which are under the control ofthe different direct current amplifiers and a third winding coupled to adriving source of alternating current energy, whereby a difference inthe outputs of said direct current amplifiers exceeding a predeterminedvalue determined by the characteristics of said limiters causes saidmotor to rotate in either of two directions depending upon the sense ofdeparture in frequency of the input alternating current waves from theresonance frequency of said tuned circuits.

3. The combination with a superheterodyne receiver including a firstdetector, a first local oscillator, a second detector and a secondvariable local oscillator, and a second intermediate frequencyamplifier, of an automatic frequency control system comprising a firstresonant circuit and a pair of discriminators comprising second andthird resonant circuits tuned to the same mid band frequency, saidsecond and third tuned circuits being inductively coupled to said firsttuned circuit, connections from the electrical center of said second andthird resonant circuits to a point on said first resonant circuit,connections from the output of said second intermediate frequencyamplifier to said first resonant circuit. a detector for eachdiscriminator comprising a pair of rectifiers connected across each ofsaid second and third resonant circuits a direct current amplifier foreach pair of rectifiers, a glow tube limiter in the output of eachdirect current amplifier, and means coupled to said glow tube limitersresponsive to the difference in the resulting direct current voltagescaused by a, variation in the frequency of the waves applied to saidfirst resonant circuit for varying the frequency of said second localoscillator in such sense and magnitude as to restore the secondintermediate frequency to the resonance frequency of said tunedcircuits.

4. The combination with a superheterodyne receiver including a firstdetector, a first local oscillator, a second detector, a second variablelocal oscillator, and a second intermediate frequency amplifier, ofanautomatic frequency control system comprising first, second and thirdresonant circuits tuned to the same mid band frequency, said second andthird tuned circuits being inductively coupled to said first tunedcircuit, connections from the electrical centers of said second andthird resonant circuits to a point on said first resonant circuit,connections from the output of said second intermediate frequencyamplifier to said first resonant circuit, a pair of rectifiers havingcorresponding electrodes connected across said second resonant circuit,another pair of rectifiers having similar corresponding electrodesconnected across said third resonant circuit, a first direct currentamplifier coupled to the outputs of one pair of rectifiers, and a seconddirect current amplifier coupled to the outputs of the other pair ofrectifiers, and a two-phase motor having different windings energized bythe different direct current amplifiers, and a third winding coupled toa driving source of alternating current energy, a link between the shaftof said motor and said second local oscillator, whereby a difference inthe outputs of said direct current amplifiers caused by a variation inthe frequency of the waves applied to said first resonant circuit causessaid motor to rotate in either of two directions depending upon thesense of departure in frequency of the applied alternat ing currentwaves from the resonance frequency of said tuned circuits.

5. In combination, a pair of vacuum tubes each having a grid and ananode, a source of control potential, connections for applying apotential from said source to one of said grids and a potential ofreverse polarity from said same source to the other grid, a glow tubefor each vacuum tube having one electrode connected to the anode of theassociated vacuum tube, and another electrode connected to a couplingvacuum tube whereby one polarity of the control potential in excess of apredetermined potential will cut off the space current through onecoupling vacuum tube while leaving unaltered the fiow of space currentthrough the other coupling tube, and vice versa, a reversible motorhaving a plurality of windings, there being a winding in series with thespace path of each coupling tube and another winding in circuit with analternating current source whereby the field currents supplied to themotor are independent of the control potentials beyond saidpredetermined value.

6. In a frequency variation response network, an alternating currentinput circuit, means including a pair of direct current amplifier tubesfor producing direct current voltages of different relative polarity inresponse to changes in the frequency of the current in said inputcircuit on opposite sides of a mean frequency, a coupling tube for eachdirect current amplifier tube, a Telechron motor having a pair ofwindings, connections from one terminal of said windings to differentoutput electrodes of said coupling tubes, a direct connection betweenthe other terminals of said windings, said direct connection extendingto a source of low frequency power, and a third winding for said motorhaving opposite terminals coupled to said source.

7. In a frequency variation response network, a first resonant circuit,a pair of discriminators each having a resonant circuit inductivelycoupled to the first resonant circuit, connections from the electricalcenters of the resonant circuits of said discriminators to a point onsaid first resonant circuit, all of said resonant circuits being tunedto the same frequency, an alternating current input circuit coupled tosaid first resonant circuit, two detectors, one for each of saiddiscriminators and each detector comprising a pair of rectifiersconnected across its associated resonant circuit, two direct currentamplifiers each followed by an individual limiter, each amplifier beingcoupled to a different one of said detectors, and means coupled to theoutputs of said limiters and responsive to the difference in theresulting direct current voltages.

8. In a frequency variation response network, a first resonant circuit,second and third resonant circuits inductively coupled to the firstresonant circuit, connections from the electrical centers of said secondand third resonant circuits to a point on said first resonant circuit,said resonant circuits being tuned to the same frequency, an alternatingcurrent input circuit inductively coupled to said first resonantcircuit, a pair of rectifiers having corresponding electrodes connectedacross said second resonant circuit, another pair of rectifiers havingsimilar corresponding electrodes connected across said third resonantcircuit, a first direct current amplifier coupled to the outputs of onepair of rectifiers and a second direct current amplifier coupled to theoutputs of the other pair of rectifiers, a limiter in circuit with theoutput of each direct current amplifier, a coupling tube having itsinput circuit connected to each limiter, and a motor having differentwindings the currents in which are under the control of the differentdirect current amplifiers and a third winding coupled to a drivingsource of alternating current energy, whereby a difference in theoutputs of said direct current amplifiers exceeding a predeterminedvalue determined by the characteristics of said limiters causes saidmotor to rotate in either of two directions depending upon the sense ofdeparture in frequency of the input alternating current waves from theresonance frequency of said tuned circuits.

9. An automatic frequency control system comprising a frequencyvariation response network having a first resonant circuit, a pair ofdiscriminators each having a resonant circuit inductively coupled to thefirst resonant circuit, connections from the electrical centers of theresonant circuits of said discriminators to a point on said firstresonant circuit, all of said resonant circuits being tuned to the samefrequency, an alternating current input circuit coupled to said firstresonant circuit, a detector for each of said discriminators comprisinga pair of rectifiers connected across its associated resonant circuit, adirect current amplifier followed by a limiter coupled to each of saiddetectors, a reversible motor having different windings energized by theoutputs from the different limiters, and a third winding coupled to adriving source of alternating current, whereby a difference in theoutputs of said limiters caused by a variation in the frequency of thealternating current input circuit causes said motor to rotate in eitherof two directions depending upon the sense of departure in frequency ofsaid input circuit from the resonance frequency of said tuned circuits.

BERS NOVIKS. CANDIDO ALBERTO VAIO.

